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 Author  Topic: Mk18 Torpedo Tube, details & usage?
Pat Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Pat Matthews  Posted on: Aug 10, 2014 - 7:01am
I'm working on another 77 footer model, a late series (PT--45 to 68), and am trying to make sense of the torpedo tubes and paraphernalia.

I think I have all the available drawings... some are more helpful than others! But for the tubes, I see a variety of configurations, primarily the number of access ports on top of the tubes. Various photos of boats seem to show variety in this detail, and I can imagine changes both at the time of installation, and possibly retrofitting of updated tubes, done simply to confuse future historians.

I'll figure something out... but right now I'm focused on the little training gears. Later Elcos had the vertically oriented gearboxes (you attached the crank to the top of the gear box). And presumably, one for each of the four tubes.

But it looks like the 77's had:

Aft tubes: No gearbox, horizontal (or angled?) approach to the training screws, with a small pedestal to support the screw just inboard of the tube.

Forward tubes: Right angle gearbox in a horizontal plane. I'm guessing here, based on one drawing that shows such a gearbox with usage stated as of "2" per boat with 4 tubes.


Next, the four support tubes (or rods) on each Mk 18: I believe I saw them referred to as "torsion tubes". If my understanding of the forward saddle is correct, this could make sense for the upper two at least.
>>> Side Rant: It amazes me-- the whole reason for these boats' existence (originally) was the torpedo... so why do we have so little documentation and photos of these darned tubes??!?)

Anyway, the forward pedestal has precision machined holes transversely through the base, which could accept a torsion bar. The torsion bar could be connected to vertical links outside the pedestal, which include:
- Tie points for the upper two long tubes;
- A head for receiving the tube's forward mounting flanges.

This mechanism could operate somewhat like the sway bar on a car. If the tube wants to grow a bit in length due to uniform thermal expansion, it could do so freely. But if one side grew (sun exposure on one side), the tube would want to go all banana in the horizontal plane. This would put a twist on my hypothetical torsion bar, counteracting the effect.
OK, this sound a little far fetched, and I'd wonder if this problem really even existed... except that I've heard that surveyors checking alignment of ships under construction can see inches of sideways bowing one way and another as the sun crosses the sky...



But anyway, to avoid reinventing this wheel, has anyone already figured out all these torpedo tube details? I've done a little searching, could easily have missed something!



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Pat Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Pat Matthews  Posted on: Aug 10, 2014 - 10:34am
FWIW and I never noticed before, the shot that Gene posted at http://pt-king.gdinc.com/images/pt%2043-7.jpg shows that the two lower tubes had a lattice between them, which again would fight sideways bowing...


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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Aug 10, 2014 - 10:59am
There were (at least) 2 different style breech doors too. The drawings have a date of October 1941 for the webbed style and April 1942 for the plain:



From PT 103:





Send me an e-mail Pat, I'll dig up what I have in the way of tube images for you.



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Patrick Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Aug 10, 2014 - 12:57pm
Thank you thank you thank you!

I've been looking for THAT shot of a tube (off and on) for over a DECADE now, never thought I'd solve the tube mount mystery, as the drawings for those particular bits seem to be missing.

Now I'm confident that that is a vertical link which can put a twisting load on the torsion bar.

I wonder- since these were Groton ordnance drawings (and not Bayonne boat dwgs), have all the right places at NARA been scoured? I have no clue if this would be a different collection than the Elco drawings...


My CAD model of a Mk 18 tube, with parts 3D printable in 1:24. A few more details to add, including the corrected torsion link.



Patrick Matthews
Matthews Model Marine
http://matthewsmodelmarine.wordpress.com/

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Patrick Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Aug 10, 2014 - 1:05pm
And yes to the different breech doors, and more: Aluminum was a strategic commodity, and manufacturers were either happy to, or encouraged to, replace it in their products with plain steel. That ribbed door, and the saddle mounts, all were cast aluminum... and later drawings show welded steel conversions, which also affected how the tubes were constructed to mate with them. No idea if/when the whole design was implemented, maybe the roll-off idea obsoleted it all.

My current employer (Ford) made many things for the war effort, including turbochargers used on B-17s and other aircraft. Ford started with GE's design, which had a cast aluminum compressor housing, and converted that to pressed steel. These were big units, and the design change freed up hundreds of thousands of pounds of aluminum for other uses.


Assembly of the stamped steel compressor housing for Ford's WW2 turbocharger:





Patrick Matthews
Matthews Model Marine
http://matthewsmodelmarine.wordpress.com/

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Pat Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Pat Matthews  Posted on: Aug 10, 2014 - 5:58pm
Jeff, I wouldn't mind seeing the rest of that 103 picture if it's bigger!

And now I kick myself... I guess I wasn't looking too hard for the last ten years, because I just found another stone that gets two of my birds... this picture is also Gene's, shows early 77s under construction. You can see the torsion bar link in the forward cradle, AND you can see the aft tube's training screw arrangement- horizontal. I still think the horizontal right angle gearbox must have been installed in the forward position.

And it likely didn't take too many busted knuckles before someone came up with the vertical axis gearbox!




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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Aug 11, 2014 - 5:47am
That is looking good Pat! It's really great to see someone make use of Al's drawings like this.

I hear you about the drawings. The PT 305 restoration crew has a local machine shop that is willing to make a pair of .50 cal. carriage and cradles for them if they can get a set of original drawings. Would you believe there is a set available, but for some reason they're not allowed to get a copy? What better reason for hanging on to the old drawings...

Those gearboxes are tough to find pictures of, thanks for pointing out Gene's. Stu Hurley and Bridge Carney did some research into the training gear, maybe they could help.

The full 103 image and a possible explanation for the 103's damage is on this thread:
http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?fid=102&cid=101&tid=2487&sc=20&pg=1&x=0

A decent shot of the 149's training gear:





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Patrick Matthews

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Post a Reply To This Topic    Reply With Quotes     Edit Message   Posted on: Aug 14, 2014 - 10:44am
OK, more Qs and As on the early Elco torpedo training gear:
Drawing 436269 (Oct/41), Torpedo Tube Foundations, shows the location of the training gear for PT20-48 & 59-68. The missing boats were BPTs iirc.

Looks like the two horizontal 90 gearboxes were AFT and for both forward and aft tubes, the linkage seems to go INSIDE the cabin!
Does this make sense, that a crewman would have to turn the crank from inside the engine room aft, and inside the trunk cabin forward? Seems very akward, especially since another crewman would be needed outside ayway to unpin and re-pin the tube stop.

Then, we have this picture on Genes site, showing a truncated forward gear:


Im supposing that if the gear went inside the cabin originally, then the kibosh was put on that idea when the deck stiffeners were added. Or maybe there was a hole? And the crank went through the cabin wall to this exposed screw-end?


Next, we have Genes shot of the (partial) aft gear:


Since DCs are installed, there is no screw-linkage.. but you can see the pedestal bearing on the torp mount pad, and in the bottom foreground, you can just see the right angle gear apparently heading into the trunk.

Elco had some good ideas, but this seriously?

Here are snips from the drawing showing the linkage locations:






Patrick Matthews
Matthews Model Marine
http://matthewsmodelmarine.wordpress.com/

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Stuart Hurley

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Stuart Hurley  Posted on: Aug 15, 2014 - 2:43am
Quote:




Those gearboxes are tough to find pictures of, thanks for pointing out Gene's. Stu Hurley and Bridge Carney did some research into the training gear, maybe they could help.






Sorry, I can't really add much to the research you have already done.
I realised during my build of 109 that the horizontal cranks were fitted to early 103 class boats. I had to rework the gearboxes and remove the speed cranks that I had fitted to the cabin roof.

Best Regards,
Stu.





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Jeff D

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Post a Reply To This Topic    Reply With Quotes     Edit Message     View Profile of Jeff D   Send Email To Jeff D Posted on: Aug 15, 2014 - 4:52am
Interesting Pat, I didn't know about the early crank linkage leading into the cabin. It probably used the short crank handles seen on the tube drawings.

The tubes would most likely be trained out well before expected action:
http://www.ptboatforum.com/cgi-bin/MB2/netboardr.cgi?fid=102&cid=101&tid=544&sc=20&pg=1&x=0
http://www.hnsa.org/doc/pt/doctrine/part6.htm




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